When an endangered northern female whale spends months, even years, disengaging from cast fishing nets, there is not much energy left for mating and cleaning carts.
Dealing with such waste, along with ship collisions and other forms of human expansion, has led to a severe recovery of royal marine mammals long after factory rings and boats nearly wiped them out, according to a study published Wednesday.
After reaching tens of thousands, the northern whale population – now 450 – has climbed slowly since 1990, but began to decline again in 2010.
If the Canadian and American waters that had survived during this quarter century were clear and unorganized in human motion, "the numbers of the species were nearly double than they are now, and their current situation was not so bad," led by Peter Corkeron of NAA North East Fisheries Science and Science Center Massachusetts.
More specifically, there will be a double number of whale women: "The overall slope of the recovery pathway prevents female mortality," the researchers added.
Between 1970 and 2009, 80% of the 122 known deaths of a whale belonging to the North Atlantic were caused by objects or human activities.
The species had not been hunted for over half a century.
The kind of nurse
But beyond the number of whales killed was the question of whether the species population could have cut back in more sophisticated ways by people.
To find out, Corkeron compared the birth rates with the Southern Right Whale, a sister species in the southern hemisphere – estimated at 15,000 – that is much better off and much less vulnerable to human emanations.
The data collected over the last three decades allowed us to count the number of new calves born in different sub-populations on both poles.
The northern and southern whales were long considered to be one species until the genetic analysis showed otherwise.
Predictably, the three groups of southern whales – from the shores of South America, South Africa, and South West Australia – produced offspring at twice the rate of their northern relatives.
Further evidence suggests that the northern Atlantic environment has claimed the low health of females and their calves, the study found.
"This female baleen whales dispense reproduction in response to specific body conditions is well established," the authors said.
What caused the cuts, reduced body weight, and alleged unwillingness to mate?
The most likely culprit is the "ghost nets", the sprawling nets of fishing gear that are usually made of strong synthetic fibers as they are long over time, the study concluded.
More than 80 percent of all the right whales of the North Atlantic are known to have an abandoned web at least once, and more than half have been there twice or more.
"The entanglement can last from months to years, and recovery can take a similar time," the authors write The Royal Open Society.
For southern whales, the problem is nonexistent.
Once numbered in hundreds of thousands, slow moving whales – migrating along the coastline – were easy and also preferred prey to whales even in the 20th century.
Species can grow to 20 feet (65 feet) and weigh 100 tons, more than a full commercial airplane.
They are also obedient and full of chess from which whale oil is made.
Endangered endangered fin on the Belgian coast
The recovery of the North Atlantic Atlantic whales, Eubalaena glacialis, was limited by human mortality, The Royal Open Society, rsos.royalsocietypublishing.or … /10.1098/rsos.180892